Automated process for recycling batches of mixed color cullet into amber, green, or flint glass with selected properties

ABSTRACT

An automated method for recycling mixed colored cullet glass (i.e., broken pieces of glass of mixed colors and types) into new glass products. A computer controlled process identifies the virgin glass raw materials, the desired target glass properties, the composition of a batch of mixed colored cullet, and the quantity of cullet to be used in the glass melt, and the computer controlled process automatically determines the proper amounts of raw materials to add to the batch of mixed colored cullet so that recycled glass is produced having the desired coloring oxides, redox agents, and glass structural oxides in the proper proportion. The recycled glass is then used to make glass products such as beer bottles.

CROSS-REFERENCE

This application is a divisional of application Ser. No. 09/057,763filed Apr. 9, 1998, now U.S. Pat. No. 6,230,521.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of glass recycling. The inventionmore particularly relates to an automated method for recycling mixedcolored cullet glass (i.e., broken pieces of glass of mixed colors andtypes) into new glass products. According to a preferred aspect of theinvention, a computer controlled process is provided whereby a recycleridentifies the virgin glass raw materials, the desired target glassproperties, the composition of a batch of mixed colored cullet, and thequantity of cullet to be used in the glass melt, and the computerprogram determines the proper amounts of raw materials to add to thebatch of mixed colored cullet so that recycled glass is produced havingthe desired coloring oxides, redox agents, and glass structural oxidesin the proper proportion. The recycled glass is then used to make glassproducts such as beer bottles.

2. Description of the Prior Art

Glass recycling involves collecting used, post-consumer glass andreusing it as a raw material for the manufacture of new glass products.A main repository of recoverable glass is glass containers such asbeverage bottles and containers for other products. Bulk recycledpost-consumer glass suitable for melting into recycled glass articles isknown as cullet. The glass cullet for recycling is generally provided inthe form of small pieces of glass.

Recycled containers comprise different colors, especially amber andgreen, and also colorless or flint glass. There also may be differenttypes of glass in the respective containers, although soda-lime-silicaglass, which primarily contains oxides of sodium, calcium and silicon,is the most prevalent. Other waste glass, e.g., off-quality material andscrap from the manufacture of glass products, may also be re-used in theform of comminuted or ground glass cullet.

Approximately ten percent (10%) of municipal refuse is glass, most ofwhich is in the form of discarded containers from beverages, foodproducts and. the like. To encourage recycling and minimize waste, thereare certain government legislated guidelines to the effect that newglass products should contain a proportion of recycled glass. There isthus a market for cullet that can be re-used readily. Unfortunately,this normally requires that the glass be sorted by color.

Municipal refuse glass is typically collected at the street, processedat a central location and ground into small particles to provide culletfor use in the manufacture of glass products. Processing can involve,for example, color sorting by hand or by optical techniques and removalof non-glass contaminants by hand, optical techniques, magnetic, eddycurrent and metal detecting separation techniques. These techniques arenot wholly effective for the separation and color sorting of all of theglass. In sorting, for example, it is possible manually, or mechanicallyby using a color sensing diverter mechanism, to sort glass by color.However, much of the glass is broken in handling and cannot readily besorted as whole containers, and sorting of smaller pieces is moredifficult. A by-product of glass recycling, even when an attempt is madeto sort the glass by color, is a quantity of mixed colored pieces.

The color distribution of the glass in post-consumer solid municipalwaste, and accordingly, in typical mixed color cullet, variesregionally. A typical color distribution is approximately 65% flint(colorless), 20% amber, and 15% green. To date, mixed colored cullet hashad only limited commercial use, and may be used as an aggregate inpaving material, landfill cover, or some similar use, but often isdiscarded in landfills. The mixed colored material is substantially lessvaluable than color sorted cullet.

Decolorizing techniques are known in the production of flint glass,especially to remove the tint due to iron impurities, which impuritiestend to impart a bluish or greenish hue to “colorless” glass. In themanufacture of colorless glass, particularly soda-lime-silica flintglasses, the presence of iron as an impurity in the raw materials hasbeen a serious problem. The presence of ferrous iron (Fe⁺²) tends tocause a bluish or blue-green discoloration in the finished glass inaddition to decreasing its overall brightness. The economics of glassmanufacture are such that it is difficult to provide low cost rawmaterials free from these iron impurities, and most significant depositsof sand and limestone contain at least trace amounts of various ironsalts and oxides.

When the raw materials are melted in the glass batch at temperatures ofabout 2,600 to 2,900 F (about 1,400 to 1,600 C), significant amounts ofiron present are converted to the ferrous (Fe⁺²) state under theinfluence of the prevailing equilibrium conditions. Decolorizers andoxidizers can be added to the glass batch in an attempt to oxidize theferrous (Fe⁺²) iron, thereby forming ferric (Fe⁺³) iron, to minimizethis glass coloration. Ferric iron (Fe⁺³) is a relatively much weakercolorant than ferrous iron.

In U.S. Pat. No. 2,929,675 (Wranau, et al.), a method is disclosed forspinning glass fibers using a fluid molten glass, which glass isoptically enhanced by decolorizing the glass to make it more transparentor translucent, so that infra-red rays of the radiant heat supply morereadily pass through the glass for heating the spinnerette. In theWranau method, glass which is naturally greenish is decolorized by theaddition of effective decolorizing amounts of such materials as seleniumoxide, manganese peroxide, copper oxide or dispersed gold to the moltenglass.

In U.S. Pat. No. 2,955,948 (Silverman), a glass decolorizing method isdisclosed which continuously produces molten color-controlledhomogeneous glass. In the Silverman method, flint (colorless) and othercontainer glass is decolorized by addition to the molten glass of aselenium-enriched frit as a decolorizing agent, as opposed to seleniumin its free state mixed with virgin batch raw materials. This isconsidered to better retain the selenium in the finished goods withoutvapor loss thereof. Silverman discloses that various commonly usedmaterials for decolorizing flint glass have been tried to eliminateselenium vapor losses without success, such as various seleniumcompounds, e.g., sodium and barium selenates and selenides, as well asarsenic, by reducing the iron oxide inherently present therein.Silverman discloses that the decolorizing agent preferably comprisesfrit compositions containing the essential decolorizing agent seleniumin its Se⁺⁴ valence state, and also may contain niter and arsenic. InSilverman's method, the decolorizing agent of selenium-enriched frit isadded to the molten flint glass and dispersed therein in order todecolorize the glass.

In U.S. Pat. No. 3,482,955 (Monks), a method is disclosed fordecolorizing the ferrous (Fe⁺²) oxide content of soda-lime glass whichnaturally contains up to about 0.1% by weight of ferrous oxide. Themethod of Monks continuously produces decolorized homogeneous glassusing a manganese-enriched frit glass as the decolorizing agent. Monks,in particular, provides a method of decolorizing soda-lime glasscontaining iron as the impurity by utilizing a decolorizing frit glasscontaining manganese that produces no undesirable coloration of its ownand adding the decolorizing frit glass to the molten base glass. Monksteaches that decolorizing frit glass preferably comprises oxidizedmanganese in the Mn⁺³ state (Mn₂O₃) and in the Mn⁺² state (MnO), whichacts as an oxidizing agent to oxidize ferrous iron to ferric iron insoda-lime glass.

Decolorizing to minimize the tint caused by trace impurities such as asmall proportion of ferrous iron is a less severe problem thandecolorizing or offsetting recycled glass that has been heavily tintedby the addition of tint producing compounds, such as chromium greenfound in high. concentrations in green glass. A sufficient treatmentwith decolorizing compositions may be difficult to achieve without alsoaffecting the clarity of the glass or causing other quality andmanufacturing problems.

In co-assigned related U.S. Pat. No. 5,718,737, a process was describedfor re-using mixed colored glass cullet to make new and useful glassproducts. As described more fully below, in the described process one ormore of the colors in the mixed colored cullet is selectively colorizedand/or decolorized to render it useful in the manufacture of glassproducts in one of the other colors. In particular, a batch of mixedcolor cullet such as recycled municipal waste glass containing a mixtureof green, amber and flint (colorless) glass, was selectively decolorizedand/or colorized to a desired color with desired properties. Forexample, the mixed colored cullet was converted to recycled ambercolored glass for the manufacture of amber glass containers, such asbeer and other beverage bottles, by selectively decolorizing for greenand colorizing to achieve an amber tint, thereby minimizing any adverseeffect on the appearance of the container due to the relatively darkamber color.

It is desired to develop a technique for automating this process forcommercial glass production whereby different batches of broken glass inmixed colors may be readily rehabilitated to provide a material that issubstantially as useful for the production of recycled glass containersas sorted amber, green, or flint glass. In particular, it is desired toexpand upon the technique described in U.S. Pat. No. 5,718,737 byautomating the recycling process and adapting it to conventionalcommercial glass production processes by specifying the amount of rawmaterials needed to create glass products with desired properties usingdifferent batches of mixed colored cullet. The present invention hasbeen designed to meet this need in the art.

SUMMARY OF THE INVENTION

An automated method for recycling mixed colored cullet glass (i.e.,broken pieces of glass of mixed colors and types) into new glassproducts in accordance with the invention meets the above-mentionedneeds in the art by providing a computer controlled process whichidentifies the virgin glass raw materials, the desired target glassproperties, the composition of a batch of mixed colored cullet, and thequantity of cullet to be used in the glass melt, and the computercontrolled process then automatically determines the proper amounts ofraw materials to add to the batch of mixed colored cullet so thatrecycled glass is produced having the desired coloring oxides, redoxagents, and glass structural oxides in the proper proportion. Therecycled glass is then used to make glass products such as beer bottles.

In particular, the present invention relates to a method of calculatingthe amount of raw materials for different mixed cullet compositions,different percentages of mixed cullet in the glass batch, and differenttarget glass compositions. Key indicator parameters for the differentglass colors are calculated and used to calculate the batch compositionto be formed from a particular cullet starting material. The results arethen printed out using, e.g., Microsoft Excel, and used in conventionalcommercial glass production processes.

A preferred embodiment of the method of creating recycled glass productsof a particular color from mixed color glass cullet having glass of atleast two different colors in accordance with the invention preferablycomprises the steps of:

selecting virgin glass raw materials and determining weight percentagesof respective components of the virgin glass raw materials;

determining weight percentages of at least the respective components ofthe mixed color glass cullet;

selecting the particular color of the recycled glass products;

specifying transmission properties of the recycled glass products of theparticular color;

determining how much of the mixed color glass cullet, by weight percent,is to be melted as a fraction of a recycled finished glass from whichthe recycled glass products are to be created;

specifying percentage composition of at least two of amber, green, andflint glass in the mixed color glass cullet;

calculating glass coloring oxide agent levels and key glass indicatorparameters of glass of the particular color with the specifiedtransmission properties;

calculating a composition of the recycled finished glass, thecomposition including weight percentages of the raw materials, the mixedcolor glass cullet, the key glass indicator parameters, and the glasscoloring oxide agent levels; and

creating recycled glass products from the calculated composition.

In accordance with the invention, if the particular color is amber, thestep of specifying transmission properties of the recycled glassproducts comprises the steps of specifying a thickness of a finishedglass product made from the calculated composition and specifying atleast two of: an optical transmission of the finished glass product at550 nm (T₅₅₀), an optical transmission of the finished glass product at650 nm (T₆₅₀), and a redness ratio (T₆₅₀/T₅₅₀) of the finished glassproduct. For amber glass, the key glass indicator parameters comprise atleast one of iron concentration, sulfur concentration, chromeconcentration, copper concentration, and oxidation state. On the otherhand, if the particular color is green, the step of specifyingtransmission properties of the recycled glass products comprises thesteps of specifying a thickness of a finished glass product made fromthe calculated composition and specifying levels of chromium and iron ofthe finished glass product. For green glass, the key glass indicatorparameters comprise at least one of chromium concentration and ironconcentration. However, if the particular color is clear, the step ofspecifying transmission properties of the recycled glass productscomprises either the step of determining the best possible neutraldensity transmission for a finished glass product for the specifiedamount of mixed color glass cullet in the finished glass product, or thestep of maximizing the amount of mixed color glass cullet used in thefinished glass product for the transmission properties specified in thetransmission properties specifying step. For clear glass, the key glassindicator parameters comprise at least one of chromium concentration,iron concentration, selenium concentration, cobalt concentration, andoxidation state.

In accordance with the preferred embodiment of the invention, the stepof calculating the composition of the recycled finished glass isperformed by a computer program loaded on a host processor, andcomprises the step of calculating the proper amounts of the respectivecomponents so that the proper coloring oxides, redox agents, and glassstructural oxides are present in the proper proportion in the finishedglass products in accordance with the following linear equation:

M _(m×n) X _(n) =B _(m)

where:

M is a matrix of dimension m by n, where n is a number of the componentsfrom which the recycled finished glass is to be made and m is a numberof composition constraints including the key glass indicator parametersplus essential oxide concentrations for the finished glass products;

X is a row vector of dimension n that defines the weight percent of eachcomponent in the recycled finished glass; and

B is a column vector of dimension m that contains target values of thecomposition constraints.

Since this linear equation may have multiple solutions, the step ofcalculating the composition of the recycled finished glass preferablycomprises the additional step of selecting solutions of the linearequation which minimize costs of the components in the recycled finishedglass if the particular color is amber or green. For example, if theparticular color is amber, the components may include compositions ofclear, amber, and green cullets plus a predetermined number ofconventional glass raw materials, and the composition constraints mayinclude concentrations of SiO₂, Al₂O₃, CaO, and Na₂O from the virginglass, the concentrations of the coloring oxides of chrome, iron,sulfur, and copper, and a chemical oxygen demand value. On the otherhand, if the particular color is clear, then the linear equation ispreferably solved by selecting the solutions of the linear equationwhich minimize iron levels in the recycled finished glass.

Preferably, the calculated composition (by weight percentages of therecycled finished glass for a predetermined amount of the finished glassproducts) and a chemical composition of the recycled finished glass, aswell as the transmission properties of the finished glass products areprinted.

The scope of the invention also includes the finished glass productsmade from the combined three mix and virgin glass composition calculatedusing the techniques of the invention. Preferably, the finished glassproduct is a glass bottle, such as an amber or green beer bottle.

The scope of the invention also includes a program storage devicereadable by a processor and storing thereon a program of instructionsexecutable by the processor during the process of creating recycledglass products of a particular color from mixed color glass cullethaving glass of at least two different colors. In accordance with theinvention, the program of instructions causes the processor to accept asinputs a designation of virgin glass raw materials, a designation of theparticular color of the recycled glass products, a designation ofdesired transmission properties of the recycled glass products of theparticular color, a designation of how much of the mixed color glasscullet, by weight percent, is to be melted as a fraction of a recycledfinished glass from which the recycled glass products are to be created,and a designation of a percentage composition of at least two of amber,green, and flint glass in the mixed color glass cullet, and causes theprocessor to determine from the inputs the weight percentages ofrespective components of the virgin glass raw materials, weightpercentages of at least the respective components of the mixed colorglass cullet, glass coloring oxide agent levels and key glass indicatorparameters of glass of the particular color with the specifiedtransmission properties, and a composition of the recycled finishedglass, the program of instructions further causing the processor tooutput an indication of the composition for use in the process ofcreating recycled glass products of a particular color from mixed colorglass cullet, the composition including weight percentages of the rawmaterials, the mixed color glass cullet, the key glass indicatorparameters, and the glass coloring oxide agent levels. The compositionis then printed for use as a “recipe” in creating finished glassproducts, such as glass beer bottles, from a glass batch including mixedcolor cullet.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will become more apparentand more readily appreciated from the following detailed description ofpresently preferred exemplary embodiments of the invention taken inconjunction with the accompanying drawings of which:

FIG. 1 illustrates the inventive technique for determining thecomposition of glass batches including post-consumer mixed color glasscullet.

FIGS. 2(a) and 2(b) together illustrate a spreadsheet of a glass oxidecalculation model from the batch formula for the creation of recycledamber glass containers from an amber melt including 35% recycled mixedcolor cullet using the techniques of the invention.

FIG. 2(c) illustrates the glass batch formulations for the creation ofrecycled green glass containers from three mix cullet typical of thatfound on the East and West Coast where substantial imported beer andwine consumption occurs, where the three mix cullet is 35% of the totalglass.

FIG. 3 illustrates the redness ratio and measured visible transmissionlevels for amber, green and clear glasses from different glassproducers.

FIG. 4 illustrates the ratio of clear (flint), amber, and green glassfor different customer glass use patterns and the products available inregional markets.

FIG. 5 illustrates the extinction coefficients for the container glassspecimens of FIG. 3 as well as the average extinction coefficients andaverage transmission normalized through 3.18 mm thick glass for themajor amber and green glass manufacturers in the United States.

FIGS. 6(a) and 6(b) respectively illustrate the glass batch formulationsfor the creation of recycled amber glass containers from a three-mixwhere the cullet is 50% and 75% of the total glass, respectively.

FIGS. 7(a)-7(c) respectively illustrate the glass batch formulations forthe creation of recycled amber glass containers from three-mix where thecullet is 25%, 50%, and 75% of the total glass, respectively, which istypical of domestic glass production.

FIGS. 8(a)-8(c) respectively illustrate the glass batch formulations forthe creation of recycled amber glass containers from the standard U.S.glass production (⅓ clear glass removed) three-mix where the cullet is25%, 50%, and 75% of the total glass, respectively.

FIGS. 9(a)-9(c) respectively illustrate the glass batch formulations forthe creation of recycled amber glass containers from the standard U.S.glass production (⅔ clear glass removed) three-mix where the cullet is25%, 50%, and 75% of the total glass, respectively.

FIGS. 10(a)-10(c) respectively illustrate the glass batch formulationsfor the creation of recycled amber glass containers from the trend toamber three-mix where the cullet is 25%, 50%, and 75% of the totalglass, respectively.

FIGS. 11(a)-11(c) respectively illustrate the glass batch formulationsfor the creation of recycled amber glass containers from the MiddleAmerica Beer Belt three-mix where the cullet is 25%, 50%, and 75% of thetotal glass, respectively.

FIGS. 12(a) and 12(b) together illustrate a spreadsheet of a glass oxidecalculation model from the batch formula for the creation of recycledgreen glass containers from a green melt including 35% recycled mixedcolor cullet using the techniques of the invention.

FIGS. 12(c) and 12(d) respectively illustrate the glass batchformulations for the creation of recycled green glass containers fromthree mix cullet typical of that found on the East and West Coast wherethe cullet is 35% and 70% of the total glass, respectively.

FIGS. 13(a)-13(c) respectively illustrate the glass batch formulationsfor the creation of recycled green glass containers from the standardU.S. glass production three-mix where the cullet is 25%, 50%, and 75% ofthe total glass, respectively.

FIGS. 14(a)-14(c) respectively illustrate the glass batch formulationsfor the creation of recycled green glass containers from the beer beltblend three-mix where the cullet is 25%, 50%, and 75% of the totalglass, respectively.

FIGS. 15(a) and 15(b) together illustrate a spreadsheet of a glass oxidecalculation model from the batch formula for the creation of recycledclear (flint) glass containers from the beer belt blend three-mix, wherethe cullet is 25% of the total glass, using the techniques of theinvention.

FIGS. 15(c) and 15(d) illustrate the glass batch formulations for thecreation of recycled clear (flint) glass containers from the beer beltblend three-mix where the cullet is 25% and 50% of the total glass,respectively.

FIGS. 16(a) and 16(b) respectively illustrate the glass batchformulations for the creation of recycled clear (flint) glass containersfrom the USA production three-mix where the cullet is 25% and 50% of thetotal glass, respectively.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

A method of recycling mixed color cullet with the above-mentionedbeneficial features in accordance with a presently preferred exemplaryembodiment of the invention will be described below with reference toFIGS. 1-16. It will be appreciated by those of ordinary skill in the artthat the description given herein with respect to those figures is forexemplary purposes only and is not intended in any way to limit thescope of the invention. All questions regarding the scope of theinvention may be resolved by referring to the appended claims.

I. MIXED CULLET RECYCLING METHOD OF U.S. Pat. No. 5,718,737

A quantity of mixed colored glass cullet may be manually recycled intonew glass products using the technique described in U.S. Pat. No.5,718,737. As described therein, the mixed colored glass cullet isgenerally reclaimed, post-consumer glass, although the glass producer'swaste cullet can also be mixed therewith, and typically comprises amixture of green glass, amber glass and flint (colorless) glass. Themixed colored cullet is primarily made of soda-lime-silica glass(otherwise referred to as “soda-lime glass”) and is typically providedin bulk in the form of a plurality of broken pieces or particlesproduced by crushing or grinding glass containers, the particlestypically sized less than 6 mm in diameter, such that the cullet can bereadily poured or otherwise handled and melted. Generally, at least onecolor may be selectively removed, neutralized, or converted in aspecified batch of mixed color glass cullet by selective physical and/orchemical decolorizing, at which time, the mixed color glass culletabsent such at least one color is recovered for use in the production ofnew glass products.

Amber colored glass may be produced from the mixed color glass cullet byselectively decolorizing the green colorant in the mixed cullet. Inparticular, the green glass particles which inherently contain chromiumoxide as the green colorant, and which also may contain iron impurities,can be selectively decolorized in the mixed colored batch to removeexcessive green which lowers the desired redness ratio or reddish hue inamber glass used to manufacture new containers, such as amber beerbottles. The reddish-brown hue of amber colored glass from mixed colorcullet is controlled by regulating the amounts of iron, carbon andsulfur in the mix to impart the desired reddish-brown amber color. Asimilar technique may be used to produce recycled green or flint coloredglass bottles and the like.

The mixed color glass cullet is optionally decolorized as to at leastone color, by addition to mixed color glass an effective amount ofdecolorizing agent(s) as provided hereinafter, for the at least onecolor to be decolorized. The method includes the step of furthercolorizing the mixed colored cullet as to at least one remaining color,by addition to the mixed colored glass, an effective amount ofcolorizing agent(s) as provided hereinafter, to enhance the remainingcolor. Preferably, a predetermined amount of mixed colored cullet glassis admixed with a virgin batch of glass containing conventional glassraw materials in the remaining color as well as decolorizing agent(s)and colorizing agent(s) to compensate for the mixed colored cullet toproduce new glass products containing a certain percentage of recycledmixed colored cullet. This is particularly effective for making amberglass containers and the like from mixed color cullet.

Conventional glass raw materials, such as those for amber, green, orflint soda-lime-silicate glasses, and glass making equipment, such asglass melting furnaces, lehrs, forming equipment and the like, can beused with the method of the invention. For a description of glass rawmaterials, glass manufacture and processing techniques, reference can bemade, inter alia, to S. R. Scholes, Ph.D., Modem Glass Practice, CBIPublishing Co., Inc. (1975) and Kirk-Othmer, Concise Encyclopedia ofChemical Technology, John Wiley & Sons, Inc. (1985), pp. 560-565, thedisclosures of which are hereby incorporated in their entireties.

Amber colored glass used for beverage bottles can be produced from thepost consumer (recycled) cullet. In such a method, a quantity of postconsumer (recycled) cullet is intimately mixed together with a virginbatch of conventional glass raw materials used for making amber coloredglass, preferably carbon-sulfur amber glass. The minimum amount of mixedcolored cullet in the batch may be affected by government regulations.It is required by some state governments to include at least about—10%or greater, while some state governments require at least about 35% orgreater, and, by the year 2000, will require between about 35% and 50%by weight post consumer (recycled) cullet in the glass. It is preferredthat the mixed colored cullet is introduced on top of a mixed virginglass in the glass melting furnace, typically operated at a temperatureof 2,600 to 2,900 F (about 1,400 to 1,600 C), to reduce the tendency ofthe cullet to cause foaming and frothing of the molten glass andresultant processing problems.

The virgin glass raw materials for amber colored glass, known to becapable of yielding glass-forming oxides, can include effective amountsof major constituents, e.g., sand, limestone, soda ash, feldspar, or thelike, and minor constituents, e.g., salt cake, gypsum, carbocite,graphite, iron pyrite, calumite, or the like.

While the precise mechanism is not well understood, the reddish-browncoloration of carbon-sulfur amber colored glass is believed to beattributed to its sulfate (e.g., soda cake and gypsum), carbon (e.g.,carbocite, graphite and carbon black) and iron (e.g., iron oxide andiron pyrite) contents. It is believed that amber glass formationinvolves the colorizing reactions of the alkali sulfates with reducingagents, such as carbon, to form alkali sulfites, elemental sulfur andsulfides, as well as alkali polysulfides and sulfoferrites, whichcompounds are all believed to play a part in the amber coloring.

Amber container glasses absorb light in the biologically active regionof 450 NM and thereby protect the container contents from chemicallyactive ultraviolet radiation. Amber glass is produced under strongreducing conditions and typically has a redox number of about −40 to −70and a redness ratio of in the range of 1.5-2.0.

The level of reduction present in a glass melting furnace is representedby the redox number, RN. The redox number is given, per ton of glass, asthe pounds of salt cake (Na₂SO₄) oxidizer equivalent in excess of thatrequired to balance the following stoichiometric equations.

C+2Na₂SO₄2Na₂O(glass)+CO₂+2SO₂

(Note that the Mass Ratio of salt cake (Na₂SO₄) to carbon (C) in thebalanced equation=284/12=23.7)

5C+4NaNO₃2Na₂O(glass)+5CO₂+2N₂

(Note that the Mass Ratio of niter (NaNO₃) to carbon (C)is=340/60=5.667, thus, the salt cake/niter ratio can be calculated by23.7/5.667=4.182)

Hence, a positive redox number indicates oxidizing conditions while anegative redox number reflects reducing conditions.

The redox number can be calculated from the following formula forbatches and glasses where all oxidizing and reducing agents areexpressed in terms of salt cake, niter, and carbon equivalents:

RN=Ss+Nn−Cc

where:

S=salt cake, lbs per ton of glass

C=carbon, lbs per ton of glass

N=niter, lbs per ton of glass

and

s=salt cake mass ratio to salt cake=1

c=salt cake to carbon mass ratio=23.7

n=salt cake to niter mass ratio=4.182

The composition of a non-limiting, purely representative example of anamber container glass (shown in weight percentages) is provided in Table1.

TABLE I Composition of Amber Colored Glass Oxide % (Wt.) SiO₂ 71-73Al₂O₃ 0.1-0.5 Fe₂O₃ 0.2-0.5 CaO 7-9 MgO 0.1-2   Na₂O 13-15 K₂O 0-1 MnO0-1 SO₃  0-.5

The mixed colored cullet may be selectively melted into the virginglass, forming a homogenous mixture. The green glass contained in themixed colored cullet, which has relatively high chromium oxide contentand which also may contain iron impurities, is decolorized by theaddition of an effective amount of a decolorizing agent to the moltenmixed colored cullet. The decolorizing agent can be a chemical orphysical decolorizing agent, or both.

In physical decolorizing, complementary colors are added to the greencullet to offset or neutralize the color green. Preferred physicaldecolorizing agents include elemental or compounds of selenium (red),manganese (red), cobalt (blue), nickel, and/or selenides. A limitationof color blending, however, is that the glass may be imparted with agray (smoky) hue in offsetting the greenness in this manner, which mayrender the glass less water-white. For a typical mixed colored culletcomprising about 56% by weight flint (colorless), 22.5% by weight amber,and 21.5% by weight green glass, it is preferred to add from about 0.001to 0.01% by weight of selenium or comparable decolorizing agent per 100%by weight mixed color cullet, most preferably between about 0.005 to0.01% by weight.

Instead of or in addition to physical decolorizing, chemicaldecolorizing can be effected. Preferred chemical decolorizing agents oroxidizing agents which can be added in effective amounts to the mixedcolor cullet to oxidize trace amounts of ferrous (green) to ferric ironinclude oxides of zinc, cerium, and arsenic, and also can includeoxidized virgin glass materials. For a typical mixed colored culletcomprising about 56% by weight flint (colorless), 22.5% by weight amber,and 21.5% by weight green glass, it is preferred to add from about 0.001to 0.01% by weight of chemical decolorizing agent per 100% by weightmixed colored cullet, most preferably between about 0.005 to 0.05% byweight.

The decolorized or color neutralized green colored cullet and the flintcullet that remain can be color enhanced to amber by adding effectiveamounts of typical colorizing agents for amber glass production.Preferred colorizing agents include iron pyrite, salt cake (sodiumsulfate), sodium sulfite, sodium sulphide, carbon (typically in the formof carbocite or graphite), and slag (typically in the form of calumite),which are used to impart a reddish-brown color. For a typical mixedcolored cullet comprising about 56% by weight flint (colorless), 22.5%by weight amber, and 21.5% by weight green glass, it is preferred to addfrom about 0.25 to 0.50% by weight of colorizing agent per 100% byweight mixed colored cullet, most preferably between about 0.30 to 0.40%by weight.

The molten mixture of mixed colored cullet converted to amber color andvirgin amber glass can be fined as is well known by the addition of,e.g., salt cake, to minimize gas bubbles therein. After fining, theglass can be directed to a glass blowing machine or other glass formingmachine in the same manner as conventionally produced glass, e.g., in abottle glass blowing machine for forming amber colored beer bottles.After forming, the glass can be annealed in a known manner, e.g., in alehr, to remove internal glass stresses.

This technique is not limited to the production of amber colored glassfrom mixed colored cullet. It is also directed to the production offlint or green glass from mixed colored cullet as well. For flint glass,a virgin batch is mixed with chemical decolorizing agents, such as,oxides of cerium and zinc to chemically oxidize iron impurities and mayalso be mixed with physical decolorizing agents having complementarycolors, such as elemental or compounds of selenium and cobalt.

This method can be better understood from the following purely exemplaryand non-limiting example.

EXAMPLE Conversion of Mixed Broken Colored Cullet to Amber Colored Glass

A batch of mixed colored cullet was suitably converted to amber coloredglass by the following method: First, about 2 lbs. of mixed coloredcullet comprising about 56% by weight flint (colorless), 22.5% by weightamber, and 21.5% by weight green glass had about 0.3 to 0.45% of Fe₂O₃equivalent by weight (based on the weight of the molten cullet) of ironpyrite added thereto and intimately mixed together therewith. From about0.015 to 0.07% by weight carbon (in the form of carbocite) was alsoadded to the mixed colored cullet to achieve a redox number ofapproximately −55. These ingredients were melted to a molten state in aglass furnace at a temperature of about 2,600° F to 2,700. The additionof carbon (reducing agent) controls the final amber color, i.e., ascarbon content increases, the reddish-brown hue increases. The moltenmixed color cullet with colorizing agents was then cooled and formedinto patty samples by pouring the molten cullet from crucibles. Theresultant glass was amber colored with UV transmittance of about 15%.

In this example, the amounts of each raw material was calculatedmanually, which is impractical since the proper control of glass colorand composition for commercial production requires the simultaneouscontrol of many variables. An automated method that provides enhancedcolor control and is suitable for commercial glass production isexplained in the next section.

II. AUTOMATED MIXED CULLET RECYCLING METHOD

In accordance with the present invention, a software algorithm has beendeveloped which facilitates the automatic calculation of the rawmaterials for different mixed cullet compositions, different percentagesof mixed cullet in the glass batch, and different target glasscompositions. In particular, key indicator parameters for the differentglass colors have been identified and are calculated using a computerprogram loaded on a host processor, and these parameters are, in turn,used by the host processor to calculate the batch composition to beformed from a particular cullet starting material. The results are thenprinted out using convenient software, e.g. Microsoft Excel, and used inconventional commercial glass production processes.

FIG. 1 illustrates the software algorithm developed in accordance withthe invention which is loaded on a host processor for calculating thecomposition of glass batches including post-consumer glass cullet to berecycled. The first part of the software algorithm of the inventionincludes the step of defining the user-selected glass parameters. Inparticular, at step 10, the user first selects from a list of optionsthe raw materials to be used for the virgin component of the glass. Inother words, the user s specifies the type and composition of sand,limestone, aplite (feldspar), source of slag (e.g., calumite), saltcake, melite, soda ash, source of carbon (e.g., CARBOCITE™ #20) and thelike to be used for the virgin glass.

At step 15, the user defines the cullet chemical composition, i.e., theoxide composition percentage of the clear, amber, and green glass in themixed cullet to be used in the recycling process.

As shown in the sample melt of FIGS. 2(a) and 2(b) for an amber meltincluding 35% recycled mixed cullet, the algorithm of the inventioninputs the oxide composition and cost of the raw materials (step 10) andthe cullet (step 15) used in preparing the batch. The oxide percentagesmay be readily determined from a chemical analysis of the materials.Typical virgin glass materials may include: Glass sand from U.S. Silica;Limestone; Aplite from U.S. Silica; Calumite from Calumite Corporation;Salt Cake; Melite; Soda Ash from FMC; and Carbocite #20. Typical culletcompositions are similar to virgin glass except that they containcoloring oxides specific for clear, green, and amber. Variousadjustments are also made for volatile loss during melting.

Next, at step 20, the user defines the color of the target glassdesired: clear (flint), amber, or green. In the glass oxide calculationexample of FIGS. 2(a) and 2(b), the specified target glass color isamber. If it is determined at step 30 that the designated color isamber, then the user should define the thickness of the transmissionspecimen (3.18 mm is the default) and specify the optical transmissionat 550 nm (T₅₅₀) and the optical transmission at 650 nm (T₆₅₀) and/orthe redness ratio, i.e., T₆₅₀/T₅₅₀, in the finished glass product atstep 32. Typical values for 550 and 650 transmission through a 3.18 mmspecimen are 11.5% and 23%, respectively. Accordingly, the default valuefor the redness ratio is 2.0.

However, those skilled in the art of glass making will appreciate thatall amber glasses are not the same. For example, as illustrated in FIG.3, the redness ratio and measured visible transmission levels for amber,green and clear glasses vary from producer to producer, and the programof the invention preferably accommodates this need. In FIG. 3, thetransmission data is adjusted to a glass thickness of 0.125 inch, or3.18 mm, which is the default thickness of the specimens, which includeamber specimens 1-6, clear specimen 8, and green specimens 7, 9, and 10.In FIG. 3, all wavelengths are in nm.

On the other hand, if it is determined at step 30 that the specifiedtarget glass color is green, then the user should define the thicknessof the transmission specimen (3.18 mm is the default) and the amount ofchromium (as Cr₂O₃) and iron (as Fe₂O₃) desired in the finished glassproduct at step 34. Typical Cr₂O₃ and Fe₂O₃ levels for green glass are0.23% and 0.25%, respectively. Greater levels produce a darker green andlesser levels a lighter color as desired for various beer and winebottles. Other coloring oxides such as Mn and Ni can be added to alterthe hue of the green glass.

If it is determined at step 30 that the specified target glass color isclear (flint), no additional input is required. The program identifiesthe amount of Fe and Cr present from the raw materials and the mandatorythree-mix cullet level and, at step 36, calculates the greatest possiblecolorless (i.e. neutral density) transmission for a given cullet inputor maximizes the amount of cullet used for a specified transmissioncharacteristic. Blue (cobalt) and red (selenium) coloring agents may beadded to give a neutral color density, i.e., nearly uniform absorptionat all wavelengths. Depending on the amount of amber and green culletused, the transmission can vary from the normal 70-80% typical of clearglass down to 30-40% for heavy three-mix loadings with lots of amber andgreen glass. Thus, some reformulated glasses will be quite gray whereasothers will be quite good flint glasses when made from three mix culletusing the techniques of the invention. A further feature of theinvention is the ability to maximize three-mix cullet use in a glassbatch. As an alternative to the above method of batching flint glass, itis possible to specify the minimum transmission of the flint glass andto have the algorithm calculate the maximum amount of a certainthree-mix cullet that will permit the specified transmission. Naturally,the calculated three-mix amount will be greater for three-mix culletswith little green and amber glass and lesser for cullets with lots ofgreen and amber.

At step 40, the user defines the quantity (%) of cullet to be used inthe melting process as a percentage of the total glass, e.g., 35, 50,75%, where the remaining material is the typical virgin glass.Typically, the total quantity of three-mix cullet is between 35% and 75%but may vary based on legislative and other requirements. In the exampleof FIGS. 2(a) and 2(b), the percentage of cullet used in the meltingprocess is designated as 35%.

At step 50, the cullet three mix ratios are specified. These valuesindicate the relative amount of clear, amber, and green glass in thecullet. These ratios may be measured by taking a core sample of themixed cullet to be recycled or may be determined empirically by glassrecyclers in different geographical areas. Typically, the ratio of clear(flint), amber, and green glass for recycling will vary according tocustomer use patterns and the products available in regional markets.Typically, as shown in FIG. 4, United States glass container productionyields approximately 60% clear (flint) glass, 30% amber, and 10% green.However, three-mix cullet compositions vary enormously depending uponcollection and recycling practices and also on consumer demographics andpreferences. Three-mix cullet flint levels are in the range of 30-60%,amber in the range of 25-55%, and green in the range of 5-25%. Moregreen tends to be present in those areas that import more foreign beersand consume more wine, as on the east and west coasts of the UnitedStates. For the example of FIGS. 2(a) and 2(b), the percentage fractionsare specified as 48.3% clear (flint), 26.7% amber, and 25.0% green, amix of cullet representative of that encountered on the east and westcoasts of the United States.

Now that all the inputs are provided, the second part of the softwarealgorithm of the invention is executed, namely, calculating the batchcomposition from the user-selected glass parameters. At step 60, thecoloring oxide ratios and glass redox levels in the glass for therequested color properties of the target glass product are computed viaknown relationships. Since soda lime glass accounts for nearly 90% ofall container glass produced, the target glass is assumed to be astandard soda lime silicate, modified with coloring oxides. For example,standard container soda lime silicate glass has the following coloringoxide percentages:

Oxide Weight Percent SiO₂ 71.5% Al₂O₃  1.7% CaO 10.9% MgO  1.5% Na₂O13.5% K₂O  0.1%

Then, at step 70, the values of key indicator parameters in the targetglass are calculated based on the user defined inputs in steps 10-50.Key indicator parameters are glass batch composition and redoxparameters that affect the color or the glass in a sensitive way. Forexample, small amounts of Cr and/or Fe will make a glass with colorranging from green to blue. The engineering and control of the color ofthe melted glass requires close control of these parameters and adetailed knowledge of the A way in which these oxides influence thecolor of the melted glass. The key indicator is parameters are differentfor the three glass colors considered herein (amber, green, and clear)and will thus be discussed separately.

Amber Glass

For amber glass, the key indicator parameters are: iron [Fe], Sulfur[S], chrome [Cr], and copper [Cu], or other red coloring agentconcentrations, and the oxidation state of the amber glass as expressedby the batch redox number or chemical oxygen demand (COD) of the glass.As known by those skilled in the art and as described previously, theredox number (RN) is a value used in commercial glass melting to expressthe redox balance between sodium sulfate (salt cake, the oxidizer) andcarbon or carbon equivalents (reducing agents). Normal redox numbers arein the range of +10 to −30 for flint and green glass and −50 to −80 foramber glass.

Chemical oxygen demand (COD), is a measure of the chemical reducingpower of batch constituents. COD is a way of measuring the redox levelof raw materials and glass using conventional methods available fromanalytical laboratories. COD is expressed as percent of carbon andrepresents, in effect, the chemical reducing power of the raw materialin terms of equivalent levels of carbon. For example, a certain carbonadditive to a glass batch may contain 78% carbon and 22% ash. Such amaterial would have a COD of 78% since it has the equivalent of 78%carbon. As a second example, a slag raw material may contain a mixtureof reduced chemical species such as sulfide and various carbides suchthat its reducing power is equivalent to 1% free carbon, even though theslag may contain no free carbon. This raw material will have a COD of1%. Hence, the COD factor, when summed over all glass batch rawmaterials, quantitatively identifies the reducing power of the batch interms of equivalent carbon levels. So, if a glass batch has a collectiveCOD of 0.2%, or 2000 ppm, then the amount of oxygen it will take up canbe calculated as follows for each 100 grams of glass:

100 grams×2000×10⁶=0.2 carbon equivalent.

C+O₂CO₂MW C=12, O₂=32

Thus, 0.2 g C “demands” 32/12*0.2=0.533 g O₂.

Those skilled in the art will appreciate that more reduced batchchemistries and higher Fe, Cr, and S levels produce darker amber glassesand that the redness ratio is increased with higher levels of S and Cu.The necessary levels of the key indicators are calculated from opticalextinction coefficients for each constituent, where the extinctioncoefficient is defined as follows:

I=I ₀ R _(f) e ^(ext L)

where I is the transmitted intensity, I₀ is the incident intensity,R_(f) is Fresnel reflection from the interfaces, ext is the extinctioncoefficient, and L is the thickness of the test specimen in mm. Forexample, Cr₂O₃ has an extinction coefficient at 550 nm of 0.484 for eachweight percent in the glass. Thus, a glass containing 0.2% Cr₂O₃ willhave an extinction coefficient attributable to Cr₂O₃ of 0.484*0.2=0.097.At 650 nm, the Cr₂O₃ extinction coefficient per percent oxide is 2.174.The other parameters are treated similarly, using values obtained fromthe literature and/or from spectrophotometric measurement.

FIG. 5 illustrates the extinction coefficients (ext) for the 10container glass specimens of FIG. 3 as calculated using the aboveequation for the different wavelengths (in rum). FIG. 5 also illustratesthe average extinction coefficients and average transmission normalizedthrough 3.18 mm thick glass for the major amber and green glassmanufacturers in the United States, where BMC is Budweiser, Miller, andCoors (for amber), and BH is Becks and Heineken (for green). Thus, thevalues used will depend on the container glass desired.

Green Glass

For green glass, the key indicators are Cr₂O₃ and Fe₂O₃ concentrations.Green glass is treated similarly to amber glass except that colormatching is done directly on an oxide basis. That is, no input regardingtransmission data is accepted, but rather the user simply defines theCr₂O₃ and Fe₂O₃ levels desired in the finished glass. Typical Cr₂O₃ andFe₂O₃ levels for green glass are 0.23% and 0.25%, respectively. MoreCr₂O₃ increases the green intensity and more Fe₂O₃ increases the greenand blue intensity, depending on oxidation level. More oxidizing Fe₂O₃glasses are greenish yellow as compared to the bluish color of reducedFe₂O₃ glass.

Clear Glass

As will be appreciated by those skilled in the art, the clear glassmodel seeks to minimize the effect of the color oxides introduced fromthe green and amber cullet. It is not possible to “bleach” the glass orremove the coloring oxides; it is only possible to minimize theirimpact. This is done by minimizing (using linear programming) the amountof coloring oxides entering the glass from the virgin batch component,oxidizing the existing iron to the ferric state, and complementing thecoloring effects of Fe and Cr (greenish) with Co (blue) and Se (red) togive a neutral density absorption, i.e., a “colorless” glass. Thus, thekey indicators for clear (flint) glass are Cr₂O₃, Fe₂O₃, selenium andcobalt concentrations, and the redox number (oxidation state of theglass).

The clear glass model operates independently of user input, aside fromthe cullet and batch parameters, and computes all values internally togive the colorless glass with the highest transmission possible. Twomodes of operation are provided: transmission optimization for a giventhree-mix cullet composition and level, and cullet optimization for agiven transmission specification. Given a certain cullet mix ratio andquantity to be used in the glass, and given the raw materials from whichvirgin glass can be prepared, the minimum coloring oxide concentrationis defined. The program of the invention seeks to calculate thecomposition which supplements the defined cullet levels so that themelted glass has minimum levels of the coloring oxides for iron [Fe₂O₃]and chrome [Cr₂O₃]. Given these levels, the program then adds sufficientdecolorizing oxides such as cobalt (e.g., 2 ppm Co per 100 ppm(Fe₂O₃+Cr₂O₃)) and selenium (e.g., 30 ppm Se per 100 ppm (Fe₂O₃+Cr₂O₃))to produce a neutral color, uniform spectral absorption (i.e.,wavelength independent transmission) across the visible wavelengthrange, whereby the glass is oxidized to a redox number in the range of+5 to +10 so that the ferrous [Fe⁺²] ions are converted to ferric [Fe⁺³]to minimize the coloring effect of the iron. Depending on the amount ofamber and green cullet used, the transmission can vary from the normal70-80% typical of clear glass down to 30-40% for heavy three-mixloadings with lots of amber and green glass. Thus, some reformulatedglasses will be somewhat gray whereas others will be quite good flintglasses. In a similar fashion, the model can be used to define themaximum amount of a certain three-mix cullet that can be used inmanufacturing a flint glass with fixed transmission specifications.

Computational Algorithm—Linear Programming

Once the key indicator parameters are defined at step 70, the batchformula (composition) can be calculated using linear programing methodsat step 80. In particular, the proper amounts of raw materials,including the specified cullet fraction and mix, are computed so thatthe proper coloring oxides, redox agents, and remaining glass structuraloxides are present in the proper proportion. The linear problem is asfollows:

M _(m×n) X _(n) =B _(m)

where:

M is a matrix of dimension m by n, where n is the number of rawmaterials, including cullet, from which the batch can be calculated andm is the number of composition constraints which include all the keyindicators plus essential oxide concentrations for the base glass. In atypical amber composition, for example, there might be 12 raw materials[n=12] consisting of three different cullets [clear, amber, and green]plus nine conventional glass raw materials such as sand, limestone, sodaash, etc. The constraints may consist of SiO₂, Al₂O₃, CaO, Na₂Oconcentrations from the base glass composition, plus the coloring oxidesof iron, sulfur, and copper concentrations, plus the redox number (RN)value, and finally a constraint that requires everything to add up to100%. This totals nine constraints. Thus, matrix M is a 9×12 matrix inthis case. Although most of these calculations are performed internallyin the program, the values of most of these constraints as well as othervariables are given on the bottom two rows of FIG. 2B.

X is a row vector of dimension n that defines the weight percent of eachraw material in the glass batch. This variable, when solved, yields thebatch composition.

B is a column vector of dimension m that contains the target values ofthe constraints. These constraints are the target properties of theglass in terms of oxide and key indicator values as discussed above.

The solution to the problem is conducted in a straight-forward mannerusing matrix algebra:

X _(n) =B _(m) /M _(m×n)

As just noted, the batch calculation procedure of the invention utilizeslinear programming to calculate batch compositions from the availableraw materials and the defined requirements of the melted glass. Thoseskilled in the art of linear programming will appreciate that linearprogramming techniques solve simultaneous linear equations. As a result,in practically all real batch calculation cases, there is not a uniquesolution but rather many solutions, arising from the fact that many rawmaterials contain common oxides. For example, sand, feldspar, slag, andcullet all contain SiO₂. This multiplicity of solutions provide a“slackness” in the model. Accordingly, the technique of the inventionincludes an algorithm at step 90 for selecting from among these numeroussolutions. The presently preferred means for performing the selection iscalled the objective function, which is an additional function which issolved to give a minimum, maximum, or target value. Most typical is forthe objective function to be a simple linear cost model in which thetotal batch cost is the sum of the cost of each raw material multipliedby the fraction of the raw material in the glass batch. Thus, theslackness in the solution is used in amber and green glasses tocalculate at step 90 a batch formula selecting raw materials thatminimize the total batch cost. In flint (clear) glass compositions, onthe other hand, the slackness is used to minimize the iron content inthe batch. That is, the computer program of the invention selects fromthe multiple solutions the one that uses the least expensive rawmaterials (for amber and green glasses) or containing a minimum of iron(for flint glass).

At step 100, once the linear problem is solved, results are printedwhich give the batch composition from raw material quantities both interms of 2000 lbs. glass and as weight percentages, the chemicalcomposition of the glass, and, for amber glass, the estimatedtransmission properties. These values can then be used quite usefully inthe production of the glass by those skilled in the glass-making art andthe final step, step 10, is to transfer these data to the glassmanufacturing operation, either manually or by computerized control tothe batch weigh-out computer. For example, the raw material amounts fora 2000 pound glass batch of amber glass with the properties specified inFIG. 2(a) are illustrated in FIG. 2(b) and in the more comprehensiveoutput shown in FIG. 2(c). Suitable spreadsheet programs and printingprograms such as Microsoft Excel may be used for this purpose.

The glass articles are then produced from the raw materials sodesignated in a conventional fashion whereby the raw materials areconverted at high temperatures to a homogeneous melt that is then formedinto the articles. In particular, the molten glass is either molded,drawn, rolled, or quenched, depending on the desired shape and use. Forexample, bottles, dishes, optical lenses, television picture tubes, andthe like are formed by blowing, pressing, casting, and/or spinning themolten glass against a mold to cool and to set in its final shape. Onthe other hand, window glass, tubing, rods, and fibers are formed byfreely drawing the glass in air (or across a bath of molten tin as inthe float process) until the molten glass sets up and can be cut tolength. Of course, other glass products such as art glass, frit, andglass laminates may also be created using conventional techniques fromrecycled glass using the techniques described herein.

In summary, the computerized method of the invention includes a computerprogram loaded into the associated memory of a host processor forproviding program instructions to the host processor to perform thesteps of:

1. inputting a raw material array (M) for n materials (sand, soda ash,limestone, etc.) with m properties (SiO₂, Al₂O₃, etc.), including threemix cullet oxide composition;

2. defining the glass type for melting: clear, amber, or green;

3. determining how much cullet (by weight percent) is to be melted as afraction of the finished glass;

4. determining the three-mix cullet composition (input percentage ofclear, amber, and green in cullet);

5. specifying transmission properties of amber glass (550 nm and 650 rumtransmission percentages are required to determine level of coloringoxides used in glass) or green glass (levels of Cr and Fe must bespecified) or determine the best glass possible for a given cullet levelfor clear (flint) glass;

6. calculating glass coloring agent levels from specified transmissionproperties using known relationships between oxide percentages andextinction coefficients;

7. once the coloring agents are computed, storing the composition of theglass in a row vector of length m, where each element corresponds to thenecessary level of SiO₂, Al₂O₃, etc., in the target glass;

8. solving the linear problem MX=B by inverting matrix M (using any ofthe accepted methods in numerical analysis, such as Gauss-Jordanelimination, or Newton-Raphson iteration methods) and multiplying bytarget vector B;

9. using slackness generated by multiple solutions to minimize cost inamber and green glasses calculation and to minimize iron levels in clearglass; and

10. printing batch composition, oxide composition, and selectedtransmission parameters for each glass.

Results of Laboratory Melts for Recycled Amber, Green, and FlintGlasses 1. Amber

To demonstrate the ability of the amber model to produce amber glass ofgood redness ratio from a three-mix cullet, a sample of three-mix cullettypical of the East and West coasts of the United States containing48.3% flint glass, 26.7% amber glass, and 25% green glass was used as35% of the total amber batch, as in the example of FIGS. 2(a) and 2(b).The target amber transmission was 11.5% at 550 nanometers and 23% at 650nanometers for a redness ratio of 2.0. The reformulation algorithmdescribed above calculated the following glass batch. Note the additionof CuO to promote redness of the amber to meet the desired redness ratioeven with the presence of 8.75% green cullet.

Raw Material grams Cullet, Clear 169.05 Cullet, Amber 93.45 Cullet,Green 87.50 Sand, US Silica 427.59 Limestone 73.07 Aplite, US Silica0.00 Calumite 89.67 Salt Cake 9.09 Melite - 40 3.81 Soda Ash, FMC 141.27Coal, Carbocite #20 0.272 Copper Oxide, CuO 0.127 TOTALS Cullet 350.00Virgin Batch 744.89 Total Batch 1094.89 Glass 1000.00 Loss on Ignition(LOI) 94.89

Note that this batch is for 1000 grams of glass rather than 2000 poundsof glass as in FIGS. 2(a) and 2(b). The calculated composition of thisglass, on a batch basis (i.e. not including volatile losses duringmelting), is:

SiO₂ 71.25%  Al₂O₃ 1.67% CaO 11.32%  MgO 1.37% Na2O 13.52%  K₂O 0.10%Fe₂O₃ 0.20% TiO₂ 0.16% S(total) 0.39% Cr₂O₃ 0.02% CuO 0.01% Total100.00%  Redox Number −51

The glass was melted by Corning Laboratory Services of Corning, N.Y.according to their standard procedure. 1000 g of glass was melted for 8hours at a maximum temperature of 1450° C. in a 1.8 liter silicacrucible in an electric furnace with an ambient (oxidizing) atmospherewithout any stirring or mixing. The oxidizing atmosphere of the meltingenvironment and the eight hour residence time produces an oxidizednon-amber surface of the melt, which when mixed with the amber glassduring the pour, lightens the color of the glass. The resultant glasswas poured to a patty, annealed and a section was cut for transmissionmeasurements. The glass has the expected glass color: a good amber and abit lighter than the target. Transmission results are summarized below:

Parameter Target Value Measured Value 550 nm transmission 11.5 16.4 650nm transmission 23.0 39.9 Redness Ratio 2.0 2.4

As a second example of the ability of the invention to produce glass ofgood redness ratio, even when large amounts of green cullet are added, asample of “two-mix” cullet containing 50% amber glass and 50% greenglass was used as 40% of the total amber glass. The target ambertransmission was 11.5% at 550 nanometers and 23% at 650 nanometers for aredness ratio of 2.0. The reformulation algorithm described abovecalculated the following glass batch.

Raw Material grams Cullet, Clear 0.0 Cullet, Amber 200.0 Cullet, Green200.0 Sand, US Silica 394.94 Limestone 55.63 Aplite, US Silica 0.00Calumite 89.47 Salt Cake 9.07 Melite - 40 2.63 Soda Ash, FMC 129.48Coal, Carbocite #20 0.0298 Copper Oxide, CuO 0.3373 TOTALS Cullet 400.00Virgin Batch 681.58 Total Batch 1081.58 Glass 1000.00 Loss on Ignition(LOI) 94.89

Note that this batch is for 1000 grams of glass rather than 2000 poundsof glass as in FIGS. 2(a) and 2(b). The calculated composition of thisglass, on a batch basis (i.e. not including volatile losses duringmelting), is:

SiO₂ 71.5% Al₂O₃  1.7% CaO 10.9% MgO 1.37% Na₂O 13.52%  K₂O 0.10% Fe₂O₃0.20% TiO₂ 0.17% S(total) 0.407%  Cr₂O₃ 0.04% CuO 0.07% Total 100.0% Redox Number −51

The glass was melted by Corning Laboratory Services of Corning, N.Y.according to their standard procedure. 1000 g of glass was melted for 8hours at a maximum temperature of 1450° C. in a 1.8 liter silicacrucible in an electric furnace with an ambient (oxidizing) atmospherewithout any stirring or mixing. The resultant glass was poured to apatty, annealed and a section was cut for transmission measurements. Theglass has beautiful amber color with excellent redness ratio. Theintensity was a bit darker than expected, a factor easily adjusted insubsequent melts. Transmission results are summarized below:

Parameter Target Value Measured Value 550 nm transmission 11.5 6.0 650nm transmission 23.0 18.1 Redness Ratio 2.0 3.02

Of course, changing the percentages of amber, clear, and green cullet inthe three-mix as well as the percentage of cullet in the total glasswill lead to different glass oxide compositions to be included in thefinal glass batch. For example, FIGS. 6-11 illustrate the glass batchformulations for the respective three-mix batch calculation scenariosset forth in FIG. 4 for use in creating recycled amber glass containersusing the techniques of the invention.

FIGS. 2(c), 6(a), and 6(b) respectively illustrate the glass batchformulations for the East/West coast three-mix where the cullet is 35%,50%, and 75% of the total glass, respectively.

FIGS. 7(a)-7(c) respectively illustrate the glass batch formulations forthree-mix approximately matching USA glass production where the culletis 25%, 50%, and 75% of the total glass, respectively.

FIGS. 8(a)-8(c) respectively illustrate the glass batch formulations forthree-mix approximately matching USA glass production but with ⅓ clearglass removed where the cullet is 25%, 50%, and 75% of the total glass,respectively.

FIGS. 9(a)-9(c) respectively illustrate the glass batch formulations forthree-mix approximately matching the U.S. glass production but with ⅔clear glass removed where the cullet is 25%, 50%, and 75% of the totalglass, respectively.

FIGS. 10(a)-10(c) respectively illustrate the glass batch formulationsfor the trend to amber three-mix where the cullet is 25%, 50%, and 75%of the total glass, respectively.

FIGS. 11(a)-11(c) respectively illustrate the glass batch formulationsfor the Beer Belt Blend where the cullet is 25%, 50%, and 75% of thetotal glass, respectively.

2. Green

To demonstrate the ability of the green model to produce suitable greenglass from a three-mix cullet, a sample of three-mix cullet typical ofthe East and West coasts of the United States containing 47.2% flintglass, 27.2% amber glass, and 25.5% green glass was used as 35% of thetotal green batch. The target composition was Fe₂O₃=0.25% andCr₂O₃=0.23%. The reformulation algorithm described above calculated thefollowing glass batch:

Raw Material grams Cullet, Clear 165.36 Cullet, Amber 95.36 Cullet,Green 89.29 Sand, US Silica 437.92 Limestone 129.97 Aplite, US Silica48.77 Calumite 0.00 Salt Cake 12.05 Melite - 40 0.37 Soda Ash, FMC.134.89 Coal, Carbocite #20 0.969 Copper Oxide, CuO 0.000 Iron Chromite,FeCr₂O₄ 4.520 Chrome Oxide, Cr₂O₃ 0.047 TOTALS Cullet 350.00 VirginBatch 769.52 Total Batch 1119.52 Glass 1000.00 Loss of Ignition (LOI)119.52

The calculated composition of this glass is:

SiO₂ 72.0% Al₂O₃ 1.67% CaO 11.3% MgO 0.25% Na₂O 13.52%  K₂O 0.19% Fe₂O₃0.25% TiO₂ 0.07% S(total) 0.35% Cr₂O₃ 0.23% Total 100.00%  Redox Number−30

The glass was melted by Corning Laboratory Services of Corning, N.Y.according to their standard procedure. 1000 g of glass was melted for 8hours at a maximum temperature of 1450° C. in a 1.8 liter silicacrucible in an electric furnace with an ambient (oxidizing) atmospherewithout any stirring or mixing. The resultant glass was poured to apatty, annealed and a section was cut for transmission measurements. Theglass was a beautiful green color, as expected. Transmission results aresummarized below:

Parameter Measured Value 450 nm transmission 14.9 550 nm transmission66.6 650 nm transmission 32.6

As in the amber example, changing the percentages of amber, clear, andgreen cullet in the three-mix as well as the percentage of cullet in thetotal glass will lead to different glass oxide compositions to beincluded in the final glass batch. For example, FIGS. 12-14 illustratethe glass batch formulations for three of the respective three-mix batchcalculation scenarios set forth in FIG. 4 for use in creating recycledgreen glass containers using the techniques of the invention.

FIGS. 12(a) and 12(b) together illustrate a spreadsheet of a glass oxidecalculation model from the batch formula for the creation of recycledgreen glass containers including East/West Coast three-mix cullet usingthe techniques of the invention.

FIGS. 12(c) and 12(d) respectively illustrate the glass batchformulations for the East/West Coast three-mix where the cullet is 35%and 70% of the total glass, respectively.

FIGS. 13(a)-13(c) respectively illustrate the glass batch formulationsfor three-mix approximately matching the U.S. glass production where thecullet is 25%, 50%, and 75% of the total glass, respectively.

FIGS. 14(a)-14(c) respectively illustrate the glass batch formulationsfor the Beer Belt Blend three-mix where the cullet is 25%, 50%, and 75%of the total glass, respectively.

3. Flint (Clear)

To demonstrate the ability of the flint model to produce clear glasswith colorless absorption of a minimum level from a batch containingthree-mix cullet, a sample of Beer Belt Blend three-mix culletcontaining 55% flint glass, 40% amber glass, and 5% green glass was usedas 25% of the total flint batch. The goal of the batch computation wasto minimize Fe₂O₃, oxidize the glass to produce the lightest colorpossible, and to complement the color of the Fe and Cr with Se and Co toproduce colorless absorption with maximum transmission.

The reformulation algorithm described above calculated the followingglass batch:

Raw Material grams Cullet, Clear 137.5 Cullet, Amber 100.0 Cullet, Green12.5 Sand, US Silica 505.0 Limestone 143.7 Aplite, US Silica 54.24 SaltCake 6.28 Soda Ash, FMC. 154.48 Ferro Cobalt Frit, 2% Co 0.4869 FerroSelenium Frit, 5% Se 15.2087 Niter, NaNO3 1.5625 TOTALS Cullet 250.00Virgin Batch 863.72 Total Batch 1113.72 Glass 1000.00 Loss of Ignition(LOI) 113.72

The calculated composition of this glass is:

SiO₂ 72.6% Al₂O₃ 1.72% CaO 11.0% MgO 0.32% Na₂O 13.9% K₂O 0.20% Fe₂O₃0.084%  TiO₂ 0.06% S(total) 0.20% Cr2O3 0.002%  Se 0.0304%  Co 0.0024% Total 100.00%  COD 10

The glass was melted by Corning Laboratory Services of Corning, N.Y.according to their standard procedure. 1000 g of glass was melted for 8hours at a maximum temperature of 1450° C. in a 1.8 liter silicacrucible in an electric furnace with an ambient (oxidizing) atmospherewithout any stirring or mixing. The resultant glass was poured to apatty, annealed and a section was cut for transmission measurements.Transmission measurements were made by Corning Laboratory Services ofCorning, N.Y. according to their standard procedure. The glass was clearflint color with a neutral absorption, as expected, with transmissionbehavior, a bit lighter than expected, as summarized below:

Parameter Measured Value 450 nm transmission 80.87 550 nm transmission81.38 650 nm transmission 79.33

As in the amber and green examples, changing the percentages of amber,clear, and green cullet in the three-mix as well as the percentage ofcullet in the total glass will lead to different glass oxidecompositions to be included in the final glass batch. For example, FIGS.15 and 16 illustrate the glass batch formulations for two of therespective three-mix batch calculation scenarios set forth in FIG. 4 foruse in creating recycled clear (flint) glass containers using thetechniques of the invention.

FIGS. 15(a) and 15(b) together illustrate a spreadsheet of a glass oxidecalculation model from the batch formula for the creation of recycledclear (flint) glass containers from the Beer Belt Blend three-mix, wherethe cullet is 25% of the total glass, using the techniques of theinvention.

FIGS. 15(c) and 15(d) illustrate the glass batch formulations for thecreation of recycled clear (flint) glass containers from the Beer BeltBlend three-mix where the cullet is 25% and 50% of the total glass.

FIGS. 16(a) and 16(b) respectively illustrate the glass batchformulations for the creation of recycled clear (flint) glass containersfrom the USA production three-mix where the cullet is 25% and 50% of thetotal glass, respectively.

The invention having been disclosed in connection with the foregoingvariations and examples, additional variations will now be apparent topersons skilled in the art. The invention is not intended to be limitedto the variations and examples specifically mentioned, and accordinglyreference should be made to the appended claims to assess the spirit andscope of the invention in which exclusive rights are claimed.

For example, those skilled in the art will appreciate that thetechniques of the invention may be used for a variety of differentvirgin glass raw materials, a variety of three-mix ratios from verysmall percentages (<10%) to 100% mixed color cullet with respect to thetotal glass in the glass batch, a variety of color combinations in thethree-mix itself, and a variety of input oxides. Also, the recycledglass container end products may have any of numerous desiredtransmission characteristics. In a preferred implementation, thetechnique of the invention is used to create recycled beer bottles fromthree-mix cullet. Conventional amber beer bottles typically have a 550nm transmission of 8-20% and a redness ratio of 1.2-3.0. One of the mostprevalent types of beer bottles in circulation in the United States isthe amber beer bottle used by Anheuser-Busch which has the followingcharacteristics: 550 nm transmission of 12-15% through a 3.18 mmspecimen, with a redness ratio of approximately 1.8 to 2.0, depending onthe level of 550 transmission. The technique of the invention may beadvantageously used to create amber beer bottles with thesecharacteristics from glass batches with varying percentages of mixedcolor cullet.

Those skilled in the art will appreciate that although amber beerbottles made from mixed color cullet using the techniques of theinvention will have the desired transmission characteristics, they canbe distinguished from conventional amber beer bottles based on thechromium (Cr₂O₃) content. In particular, those skilled in the art willappreciate that amber and clear bottles made from mixed color culletincluding measurable amounts of green cullet will have chromium levelswell above the trace chromium contamination levels which wouldordinarily be expected from the use of chrome-containing refractories inglass furnaces or from other sources of chromium contamination. Sincechromium is relatively expensive, it is not likely to be introduced intothe glass in measurable quantities from other sources. In accordancewith the invention, amber bottles made from mixed color cullet includinggreen glass may have a chromium weight percent in a wide range of 0.01%to 0.3%, although narrower ranges such as 0.015% to 0.15% or 0.015% to0.10% may also be measured. In the samples given above, the chromiumrange was 0.02% to 0.04%. Of course, the weight percentages for chromiumwill vary as the amount of green cullet in the mixed color culletvaries.

All such variations are intended to be included in the following claims.

I claim:
 1. A program storage device readable by a processor and storingthereon a program of instructions executable by said processor duringthe process of creating recycled glass products of a particular colorfrom mixed color glass cullet having glass of at least two differentcolors, said program of instructions causing said processor to accept asinputs a designation of virgin glass raw materials, a designation ofsaid particular color of said recycled glass products, a designation ofdesired transmission properties of said recycled glass products of saidparticular color, a designation of how much of said mixed color glasscullet, by weight percent, is to be melted as a fraction of a recycledfinished glass from which said recycled glass products are to becreated, and a designation of a percentage composition of at least twoof amber, green, and flint glass in said mixed color glass cullet, andcausing said processor to determine from said inputs the weightpercentages of respective components of said virgin glass raw materials,weight percentages of at least said respective components of said mixedcolor glass cullet, glass coloring oxide agent levels and key glassindicator parameters of glass of said particular color with saidspecified transmission properties, and a composition of said recycledfinished glass, said program of instructions further causing saidprocessor to output an indication of said composition for use in theprocess of creating recycled glass products of a particular color frommixed color glass cullet, said composition including weight percentagesof said raw materials, said mixed color glass cullet, said key glassindicator parameters, and said glass coloring oxide agent levels.
 2. Aprogram storage device as in claim 1, wherein said program ofinstructions causes said processor to calculate the proper amounts ofsaid respective components so that proper coloring oxides, redox agents,and glass structural oxides are present in the proper proportion in thefinished glass products in accordance with the following linearequation: M _(m×n) X _(n) =B _(m) where: M is a matrix of dimension m byn, where n is a number of said components from which said recycledfinished glass is to be made and m is a number of compositionconstraints including said key glass indicator parameters plus essentialoxide concentrations for said finished glass products; X is a row vectorof dimension n that defines the weight percent of each component in saidrecycled finished glass; and B is a column vector of dimension m thatcontains target values of said composition constraints.
 3. A programstorage device as in claim 2, wherein said program of instructionscauses said processor to select solutions of said linear equation whichminimize costs of said components in said recycled finished glass.
 4. Aprogram storage device as in claim 2, wherein said program ofinstructions causes said processor to select solutions of said linearequation which minimize iron levels in said recycled finished glass. 5.A program storage device as in claim 2, wherein said program ofinstructions causes said processor to print said composition by weightpercentages of said recycled finished glass for a predetermined amountof said finished glass products and a chemical composition ofsaid,recycled finished glass.
 6. A program storage device as in claim 2,wherein said program of instructions causes said processor to printestimated transmission properties of said finished glass products.